1. Field of the Invention
This invention relates to packages for integrated circuits, and in particular a process and the resulting structure for fabricating precision optical spacers of desired thickness to separate a window or filter from an image sensor such as a charged coupled device.
2. Brief Description of the Prior Art
Several techniques have been used to fabricate a precision optical spacer for separating an image sensing device from a filter or window. One prior art technique has been to utilize mechanical spacers, for example, precision machined material, to dispose between the image sensor and the overlying filter or window. Such techniques have typically been expensive, difficult to fabricate in applications where very thin spacers are required, and difficult to handle and align.
Another prior art technique has been to deposit metal or other material directly on the surface of the integrated circuit and attempt to form the material to the desired thickness. Such techniques require several extra masks during the fabrication of the image sensor or other integrated circuit, resulting in a lower overall yield. Additionally, such techniques make back lapping the substrate on which the integrated circuit or image sensor is formed difficult, and frequently result in cracking of the sensor during back lapping.
A third prior art approach has been to design precision packages for containing the image sensor. Such packages typically require extremely careful manufacturing processes, with accordingly high cost.